1. Field of the Invention
The present invention relates to a two-stage erbium doped fiber amplifier (EDFA) using remnant pumping light, and more particularly, to a two-stage EDFA wherein a front-stage EDFA is excited using remnant pumping light after a rear-stage EDFA is excited, thereby amplifying signal light.
2. Description of the Related Art
In an optical transmission system, an erbium doped fiber amplifier(EDFA) directly amplifies an optical signal that has been weakened during transmission without converting the optical signal into an electrical signal, thus remarkably extending the transmission distance. U.S. Pat. No. 5,768,012 to Raymond Zanoni et al. entitled Apparatus And Method For The High-Power Pumping Of Fiber Optic Amplifiers and U.S. Pat. No. 5,673,129 to Victor Mizrahi entitled WDM Optical Communication Systems With Wavelength Stabilized Optical Selectors are examples of known optical amplifiers.
FIG. 1 shows a structure in which a optical signal is amplified by the above-mentioned two-stage EDFA. The EDFA shown in FIG. 1 includes an input connector 100, a first divider 110, a first photodiode 120, a controller 130, a first pumping source 140, a first erbium doped fiber amplifying unit 150, a second pumping source 160, a second erbium doped fiber amplifying unit 170, a second divider 180, a second photodiode 190, and an output connector 195.
The operation of the EDFA is as follows. When optical signal is input through the input connector 100, the first divider 110 divides the optical signal according to a predetermined ratio. The first photodiode 120 converts the divided optical signal from the first divider 110 into an electrical signal and outputs the electrical signal to the controller 130. First pumping light generated by the first pumping source 140 is multiplexed with optical signal in the first erbium doped fiber amplifying unit 150. In this way, the first erbium doped fiber amplifying unit 150 amplifies the optical signal in response to the first pumping light. Second pumping light generated by the second pumping source 160 is multiplexed with optical signal amplified by the first erbium doped fiber amplifying unit 150. In this way, the second erbium doped fiber amplifying unit 170 re-amplifies the amplified optical signal in response to the second pumping light. The second divider 180 divides optical signal that has been re-amplified by the second erbium doped fiber amplifying unit 170 according to a predetermined ratio. The second photodiode 190 converts the divided optical signal into an electrical signal and outputs the electrical signal to the controller 130. The controller 130 controls the amplification factor of the first and second optical fiber amplifiers 150 and 170 by checking the intensity of optical signal from the electrical signal output from the first and second photodiodes 120 and 190 and controlling the intensity of pumping light of the first and second pumping sources 140 and 160.
Since two pumping sources are used in such a two-stage EDFA, the efficiency of the pumping light is low.